Repaint rebuilds one time window of a track and leaves everything outside it untouched, on the full-size ACE-Step 1.5 checkpoint. Set start and end in seconds, describe the new music, and the section regenerates in context, duration preserved: swap a chorus, rework an intro, replace a solo. To change sung lyrics in the window, start the prompt with "Repaint the selected section with new sung lyrics:", pass the full lyric sheet with the new section in place, and turn Thinking off. For fast passes at half the cost, use ACE-Step 1.5 Repaint Turbo.